fix(grafana): stop the tenant stat panels double-counting every total

[tompscanlan]

fix(grafana): stop the tenant stat panels double-counting every total

The four "Total" stat panels on the metrics dashboard were showing exactly
twice the real number. Measured against live prod Prometheus:

Total Users 4996 -> 2498
Total Groups 312 -> 156
Active Users (30d) 418 -> 209
Total Events 30824 -> 15412

MetricsService exports each gauge once per tenant AND once more with
tenant="all" as a pre-aggregated total (metrics.service.ts sets the per-tenant
label in the collect loop and then sets tenant="all" from the accumulated
totals). So the tenant label space is {all, , , ...} and

sum(max by (tenant) (users_total{...}))

adds the "all" rollup to the per-tenant series it is already the sum of --
double-counting by construction, and it would have kept reading exactly 2x no
matter how many tenants existed.

Excluding the rollup from the sum fixes it. Each corrected expression now
equals max(...{tenant="all"}) exactly, verified for all four metrics against
prod. Keeping the sum-over-tenants form rather than switching to
max(...{tenant="all"}) preserves the $tenant template variable: selecting a
single tenant still shows that tenant's number, which a bare "all" lookup would
break.

openmeet-performance.json was already correct -- it uses
max(...{tenant="all"}) -- which is why the two dashboards disagreed by 2x on
the same metric.

Unrelated to the cron duplication fixed in b4212d2. That changed how OFTEN the
rollup ran, not the values, and these panels have read double since the
tenant="all" series was introduced.

NOTE: these dashboards are not provisioned -- no ConfigMap in the monitoring
namespace contains these expressions, so Grafana holds a manually imported
copy. This commit fixes the file in git; the running dashboard keeps showing
2x until someone re-imports it.

Verification

All four corrected expressions checked against live prod Prometheus and each now equals max(...{tenant="all"}) exactly:

panel	before	after	truth
Total Users	4996	2498	2498
Total Groups	312	156	156
Active Users (30d)	418	209	209
Total Events	30824	15412	15412

jq -e . confirms the file is still valid JSON. Diff is 4 lines.

Follow-up needed (not code)

These dashboards are not provisioned — no ConfigMap in monitoring contains these expressions, so the running Grafana holds a manually imported copy. It will keep showing 2x until the dashboard is re-imported.